Polar bear-sized 'mosaic' dinosaur found with tiny T-rex arms

A newly discovered dinosaur had tiny arms resembling those of a T-rex, despite the fact the prehistoric creature evolved independently from the iconic beast.

The Gualicho shinya, which the team describes as a "mosaic dinosaur" was found in Patagonia and has similar limbs to those of the distinctive T-rex; short, with two-fingered claws. This is despite the fact it is not related to the animal, and on a different branch of the theropod family tree.

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"Gualicho is kind of a mosaic dinosaur, it has features you normally see in different kinds of theropods," said corresponding author Peter Makovicky.

"It's really unusual — it's different from the other carnivorous dinosaurs found in the same rock formation, and it doesn't fit neatly into any category."

Gualicho is an allosaurid, and though the team has not discovered its entire skeleton, it believes it was of a medium size; the researchers compare it to a polar bear. But despite this, the Gualicho's arms were "the size of a human child's" and it had just two digits.

"By learning more about how reduced forelimbs evolved, we may be able to figure out why they evolved," said Makovicky.